Method and apparatus for performing in file slider take-off measurements through tuned external AE detection

Abstract

An acoustic emission technique and apparatus that determines the take-off velocity of a slider based upon a quantitative measurement of slider velocity without internal access to the file. The system includes a vibration detector for detecting contact energy, and for producing an output signal; and a logic circuit coupled to the vibration detector, for processing the output signal from the vibration detector to identify a slider take-off velocity. The slider take-off velocity is derived by multiplying lambda by the characteristic frequency, where lambda is the spacing between bumps in a circumferential direction. The output signal of the vibration detector disappears when the slider clears the landing zone. The vibration detector is attached to the actuator screw or other vibration transfer features accessible from outside the disk drive.

What is claimed is: 
     
       1. A slider take-off velocity determination apparatus, comprising: a vibration detector for detecting contact energy between a slider and projections of a known spacing on a disk surface and for producing an output signal having a frequency component corresponding to the rate that the slider contacts the projections; and   a logic circuit, coupled to the vibration detector for processing the output signal from the vibration detector to identify a slider take-off velocity, the slider take-off velocity corresponding to the velocity of the slider relative to disk where the slider glides above the projections without contacting the projections.   
     
     
       2. The apparatus of claim 1 wherein the slider take-off velocity is derived by multiplying lambda by the characteristic frequency, where lambda is the spacing between projections in a circumferential direction. 
     
     
       3. The apparatus of claim 1 where the output signal of the vibration detector disappears when the slider clears the disk surface. 
     
     
       4. The apparatus of claim 1 wherein the vibration detector is attached to a vibrating structural feature of the disk drive accessible from outside the disk drive. 
     
     
       5. The apparatus of claim 1 wherein the vibration detector comprises an acoustic emission (AE) sensor, an accelerometer, or a laser doppler vibrometer. 
     
     
       6. The apparatus of claim 1 wherein the acoustic emission sensor is attached to a vibrating structural feature of the disk drive accessible from outside the disk drive. 
     
     
       7. The apparatus of claim 6 wherein the actuator screw is accessible through an opening in an enclosure enclosing the disk drive. 
     
     
       8. The apparatus of claim 1 wherein the logic circuit comprises a frequency filter having a predetermined cut-off frequency to signal when all sliders in the disk drive have not taken off at the predetermined cut-off frequency. 
     
     
       9. The apparatus of claim 1 wherein the logic circuit comprises a filter adjusted to a fixed frequency corresponding to a desired slider take-off velocity, thereby acting as a go/no-go indicator. 
     
     
       10. The apparatus of claim 1 wherein the projections of a known spacing comprise laser bumps. 
     
     
       11. The apparatus of claim 10 wherein the laser bumps are disposed in a landing zone of a textured disk surface. 
     
     
       12. A disk drive system, comprising: a disk having a recording area and a landing zone, the landing zone including projections of a known spacing for providing a durable, low stiction region for start/stop operation;   a magnetic sensor including a slider and magnetic head, operatively coupled to the disk, for reading data from and writing data to the recording area;   a suspension assembly, coupled to the magnetic sensor, for supporting the magnetic sensor;   an actuator assembly, coupled to the suspension assembly, for controlling the movement of the magnetic sensor relative to the disk, the actuator assembly positioning the magnetic sensor over the landing zone prior to a stop operation;   a vibration sensor, coupled to the actuator assembly, for detecting energy associated with contact between the slider and the projections in the landing zone upon spinup of the disk; and   logic circuit, coupled to the vibration sensor, for receiving a signal from the vibration sensor having a characteristic frequency component representing the energy and processing the signal to identify a take-off velocity.   
     
     
       13. The disk drive system of claim 12 wherein the slider take-off velocity is derived by multiplying lambda by the characteristic frequency, where lambda is the spacing between projections in a circumferential direction. 
     
     
       14. The disk drive system of claim 12 where the output signal of the vibration sensor disappears when the slider clears the landing zone. 
     
     
       15. The disk drive system of claim 12 wherein the vibration sensor is attached to a portion of the actuator assembly accessible from outside the disk drive. 
     
     
       16. The disk drive system of claim 12 wherein the vibration sensor comprises an acoustic emission (AE) sensor, an accelerometer, or a laser doppler vibrometer. 
     
     
       17. The disk drive system of claim 12 wherein the acoustic emission sensor is attached to a vibrating portion of the disk drive accessible from outside. 
     
     
       18. The disk drive system of claim 17 wherein the vibrating portion is accessible through an opening in a cover of the disk drive. 
     
     
       19. The disk drive system of claim 12 wherein the logic circuit comprises a frequency filter having a predetermined cut-off frequency to alert when the slider in the disk drive has not taken off at the predetermined cut-off frequency. 
     
     
       20. The disk drive system of claim 12 wherein the logic circuit comprises a filter adjusted to a fixed frequency corresponding to a desired take-off velocity, thereby acting as a go/no-go indicator. 
     
     
       21. The disk drive system of claim 12 wherein the projections of a known spacing comprise laser bumps. 
     
     
       22. A method of determining a slider take-off velocity, comprising the steps of: detecting contact energy between a slider and projections of a known spacing in a landing zone of a disk using a vibration detector;   producing an output signal for the vibration detector having a frequency component corresponding to the rate that the slider contacts a projections in the landing zone; and   processing the output signal from the vibration detector to identify a slider take-off velocity.   
     
     
       23. The method of claim 22 wherein the slider take-off velocity corresponds to the velocity of the slider relative to disk where the slider glides above the projections without contacting the projections. 
     
     
       24. The method of claim 22 further comprising the step of deriving the slider take-off velocity by multiplying lambda by the characteristic frequency, where lambda is the spacing between projections in a circumferential direction. 
     
     
       25. The method of claim 22 further comprising the step of associating the disappearance of the output signal of the vibration detector with the slider clearing the landing zone. 
     
     
       26. The method of claim 22 wherein the step of detecting contact energy further comprises attaching the vibration detector to a portion of an actuator assembly accessible from outside the disk drive. 
     
     
       27. The method of claim 22 wherein the actuator assembly is accessible through an opening in a cover of the disk drive. 
     
     
       28. The method of claim 22 wherein the vibration detector comprises an acoustic emission (AE) sensor, an accelerometer, or a laser doppler vibrometer. 
     
     
       29. The method of claim 22 wherein the processing step further comprises the step of filtering the output signal through a frequency filter having a predetermined cut-off frequency to alert when the slider in the disk drive has not taken off at the predetermined cut-off frequency. 
     
     
       30. The method of claim 22 wherein the processing step further comprises the step of filtering the output signal through a filter adjusted to a fixed frequency corresponding to a desired take-off velocity, thereby acting as a go/no-go indicator.